U.S. Pat. Nos. 3,854,874 and 3,904,361 describe a process for sterilizing a web of packaging material by dip coating the web in a concentrated solution (10% to 40%) of hydrogen peroxide and then quickly evaporating the liquid film within 20 seconds as it travels through a hot chamber at temperatures of 80.degree. C. to 120.degree. C. where some hydrogen peroxide gas is generated for contact with the web.
Submersion of the web in concentrated liquid hydrogen peroxide solution would cause a "shock" effect on microorganisms making them eaiser to kill in the hot chamber. Also at 80.degree. C. heat alone starts to become sporicidal and its sporicidal activity increases with temperature. It is noted that steam sterilization is carried out at 120.degree. C. to 125.degree. C. Although hydrogen peroxide gas is generated for contact with the packaging web, it is believed that sterilization occurs primarily because of the combined liquid and heat treatment.
Temperatures below 80.degree. C. are generally considered nonsporicidal and a "cold" sterilizing process would operate in this range. The conventional ethylene oxide gas sterilization process is considered a "cold" process and typically operates at about 55.degree. C.
The processes shown in the above two patents reduce viable bacterial spore population by only 5 log orders. The Food and Drug Administration (FDA) is currently recommending that all medical and surgical products be sterilized to a probability of survival for spores, which are the most resistant of cells to kill, of 10.sup.-6 or better. This means that the sporicidal activity of a sterilizing process must be so reliable as to assure the probability of less than 1 organism out of 1,000,000 will survive a sterilization cycle.
A "cold" sterilizing process that has produced survival probability sufficient for sterile medical and surgical products utilizing hydrogen peroxide gas has been described in a Moore and Perkinson patent application, Ser. No. 639,966, filed Dec, 11, 1975, and now abandoned. Such process operates at below 80.degree. C. without requiring submersion in a concentrated hydrogen peroxide solution. Nothing is disclosed in such process relating to the space sterilized or the concentration of hydrogen peroxide in the gas phase. It is noted that the conventional ethylene oxide process is typically run at 55.degree. C. with a gas phase concentration of 630 mg/L.